1. Field of the Invention
This invention relates to a device for automatically feeding sheets one by one to an image processing device such as a copying machine, and more particularly to a high-performance sheet feeding device provided with abreast sheet stackers for accommodating a mass of sheets so as to rationally feed the sheets from one selected from the sheet stackers to various image processing devices.
2. Description of the Prior Art
Attendant on an image processing device typified by a copying machine and printer which handles sheets such as copying and printing papers, not infrequently, there have been used ancillary sheet feeding devices for storing a mass of sheets and feeding the sheets one by one to the image processing device. To lessen the labor of loading the image processing device or sheet feeding device with the sheets which often becomes onerous, mass-storage sheet stackers capable of loading a large quantity of sheets at a time have come to be adopted to the image processing device. The sheet feeding devices of this type by and large have a plurality of sheet stackers for storing stacks of sheets of different sizes or the same size.
According to the arrangement of the sheet stackers, the ancillary sheet feeding device to be attached to the image processing device may be classified for convenience sake into a horizontal abreast type (e.g. Japanese Patent Application Public Disclosure No. HEI 5-97262(A)), a vertically arranged type (e.g. Japanese Pat. Appln. Pub. Discl. No. HEI 60-6538(A)), and a composite type (e.g. Japanese Pat. Appln. Pub. Discl. No. HEI 2-204237(A)).
Any type of sheet feeding device with a plurality of sheet stackers has a function of switching the sheet stackers so that, when one of the sheet stackers becomes empty of sheet, the sheets contained in the other sheet stacker can be sent out one by one in succession. To fulfill such a function, the conventional sheet feeding device is generally formed simply by arranging two or more sheet stacker units side by side which each have sheet transferring means so as to send out the sheets one by one by itself. Thus, the sheet feeding device formed merely by combining sheet stacker units capable of functioning independently becomes bulky double or more as many as a sheet feeding device having a single sheet stacker unit, and is complicated because each stacker unit necessitates a sheet transfer path leading to a sheet discharge port of the sheet feeding device and other independent elements for the exclusive use of the respective sheet stackers.
In general, the sheet stacker units mounted in the sheet feeding device each possess sheet separating means ordinarily formed of a pair of rollers for permitting one sheet to pass therethrough in addition to the sheet drawing-out means for drawing out the sheet from the stacker. Accordingly, there has been so far a limit in making the sheet feeding device compact because the adjoining sheet stacker units with the respective sheet drawing-out means and sheet separating means cannot be disposed close to each other.
To be more specific, the typical of the conventional sheet feeding device of the horizontally abreast type of which an image processing device M such as a copying machine comprises first and second sheet stackers 2a and 2b placed side by side as schematically shown in FIGS. 1(A) and 1(B). The sheet feeding device of this type is disclosed in the aforenoted Japanese Pat. Appln. Pub. Discl. No. HEI 5-97262, for instance.
The first and second sheet stackers 2a and 2b in the sheet feeding device 1 each have an elevating tray 3 on which a stack of sheets SS are placed, a sheet draw-out roller 5 for drawing out the uppermost sheet of the stack of sheet SS, and a pair of sheet separation rollers 6 disposed nearby the sheet exit of the stacker for permitting only one sheet to pass therebetween to prevent a so-called "double-feed phenomenon."
When giving an image processing command to the image processing device M, the sheet draw-out roller 5 of the first stacker 2a is operated to draw out the uppermost sheet from the stacker 2a. The sheet drawn out from the stacker 2a is sent to the sheet discharge port 7 through the sheet separation rollers 6 and a first transfer path P1 and introduced into the image processing device M.
The stack of sheets SS on the elevating tray 3 in the first stacker 2a is elevated with successive sheet feeding operation, so that the uppermost of the sheets SS stacked on the tray 3 is always situated at an upper sheet send-out position so as to come into contact with the draw-out roller 5.
When the first sheet stacker 2a becomes empty of sheet, the sheets SS in the second sheet stacker 2b are uninterruptedly sent out one by one by driving the draw-out roller 5 and the sheet separation rollers 6 of the second sheet stacker 2b as shown in FIG. 1(B). The sheet drawn out from the second sheet stacker 2b is delivered along a second transfer path P2 and introduced into the image processing device M via the sheet discharge port 7.
As is apparent from the above, every sheet stacker disposed in the conventional sheet feeding device necessitates individual sheet sending-out means including the draw-out roller, the sheet separation rollers and the transfer path with some pair of feeding rollers 8 for the exclusive use thereof. Thus, the aforenoted structure in the conventional sheet feeding device is disadvantageously complicated and can by no means materialize miniaturization of an image processing system.